Optimization of surgical management of spinal deformity and the development of new surgical techniques are hampered by the difficulties of conducting scientific studies in a human population undergoing surgery. Much of the scientific basis for the design of surgical implants and instrumentation comes from investigations of animal or cadaver spines, so its relevance to real surgical cases is questionable. Approximately 100,000 spinal fusions were performed in non-Federal hospitals in the USA in 1986. Postoperative problems of spinal fusions include residual or iatrogenic deformity, pseudoarthrosis in fusions, and instrumentation failure. This study is based on the premise that postoperative problems can be reduced if the surgery can be simulated in advance by means of a mathematical analysis. The simulations will show how to manipulate variable factors to maximize correction of the deformity and to maximize rigidity of the spinal fixation. This proposed series of investigations will use a sophisticated computer model of the mechanical properties of the deformed spine and rib cage to predict changes in its shape and flexibility with application of the instrumentation systems in common use, with variations in the method of application. A series of 40 patients undergoing such surgery for scoliosis deformity, and 40 patients undergoing surgery for spinal injury or instability secondary to degenerative changes will provide measurements of the 3-D shape of the spine and thorax pre- and post-surgery. Bending films will provide measurements of the spinal range of motion. Results of surgery will be compared with the model simulation of the particular surgical procedure which was chosen. Further validation of the developed model will be made by simulating various instrumentations applied to excised animal spines, and the results will be compared to laboratory biomechanical studies. The results of these investigations will be used eventually to quantify mechanical behavior of existing and new instrumentation systems, as well as to simulate variations in surgical technique for individual cases to assist in planning of surgery. Results will help to provide guidelines for selection and use of different surgical procedures.